1. Field of the Invention
The present invention relates to a drive unit for driving wheels of a vehicle toy, and more particularly to a drive unit for controlling, in travelling, a vehicle toy such as tanks provided with caterpillars and like vehicles.
2. Description of the Prior Art
In conventional remote-controlled vehicle toys, there are known vehicle toys such as tanks (war vehicles) provided with caterpillars (such as endless tracks and the like) and like vehicles. Since this vehicle toy travels by means of caterpillars running round front left-hand/right-hand and rear left-hand/right-hand wheels, a ground contact area of the vehicle is large to substantially prevent the vehicle from being stuck, and, therefore enable the same to perform off-road travelling on sands, grasslands and the like. Such vehicle toy provided with the caterpillars is provided with a drive mechanism for driving a left-hand and a right-hand wheel, respectively, and uses a zero turning radius system which uses a difference in rotation between the caterpillars when the vehicle makes a turn by having the left-hand and the right-hand rear wheel rotate in directions opposite to each other.
Since the conventional vehicle toy provided with the caterpillars drives its caterpillars, the vehicle has a large ground contact area resulting in a large frictional resistance. Particularly, when the vehicle makes a turn, a load on the vehicle becomes very large. Due to this, for example, even when the vehicle uses a high-performance motor and a high-power nickel-cadmium battery and the like, it suffers from poor torque when the vehicle employs a low gear ratio to realize a high-speed performance. On the other hand, when the vehicle employs a high gear ratio to realize a large-torque performance, it suffers from poor speed. Namely, in the conventional caterpillar vehicle toy, it is difficult to realize an adequate performance having high-speed performance and large-torque performance both compatible with each other. Further, should both high-speed and large-torque performances be simultaneously realized, the battery life would be extremely reduced, which would be very disadvantageous.